A wire line core barrel inner tube assembly having overshot coupling mechanism.
In dry hole coring operations wherein the drilling direction is predominately downwardly, it is frequently necessary to use an overshot assembly for lowering a wire line core barrel inner tube assembly to prevent damage to the inner tube assembly that would result from allowing it to free fall to the bit end of the drill stem. In using conventional overshot assemblies in conjunction with an overshot latch release tube for decoupling the overshot assembly from the inner tube assembly when the inner tube assembly is adjacent the bit end of the drill stem, if the inner tube assembly should suddenly "hang-up" in the drill stem while being lowered, due to inertia of the overshot assembly, the latch release tube, at times, will prematurely move relative the overshot assembly to operate the overshot assembly lifting dogs (or similar members) from a coupling attachment with the inner tube assembly. As a result the inner tube assembly will be prematurely released and the inner tube assembly can drop to the bottom of the drill string in a free fall condition causing a potentially dangerous or damaging situation.
In U.S. Pat. No. 1,427,268 to Dodd there is disclosed a latch release member slidably extended through a head, for moving overshot jaws to a release position, the release member having an overshot coupling head. When using an overshot assembly for lowering the core barrel inner tube assembly of Dodd's, at times the overshot jaws will not move downwardly relative the release head sufficiently to move the jaws to an inner tube assembly release position, and as a result the core barrel inner tube assembly may have to be partially withdrawn and lowered a number of times before the inner tube assembly is released. Also there is no assurance that upper latches are properly seated when the inner tube assembly of Dodd's is released and the overshot assembly withdrawn.
In U.S. Pat. No. 3,004,614 to Janson et al., there is disclosed an overshot assembly having a locking coupling that includes detent balls for couplingly engaging the spear point head of a core barrel inner tube assembly. However, the latches for retaining the inner tube assembly in a core taking position are mounted in the drill stem. As a result the drill stem has to be withdrawn when ever the latches have to be replaced, this being undesirable.
In U.S. Pat. No. 3,225,845 to Koontz et al., there is disclosed an overshot assembly having a locking coupling that includes detent pins for couplingly engaging the spear point head of a core barrel inner tube assembly, the spear point head forming an integral part of the device for releasably locking the inner tube assembly balls in a latch seat engaging position. In the event this system is used in a drill stem of an inner diameter large enough for the inner tube assembly balls to move outwardly to a latch seat engaging position prior to these balls being radially opposite the drill stem latch seat, the inner tube assembly can be prematurely released.
In order to avoid problems such as the above, as well as others, this invention has been made.